table   {border: 1px solid gray;}
pre     {background-color: #f0f0f0;}
.top_table
        {border: none; background-color: #f1f1f1;}
.navigation_table
        {border: none;}
.navigation_cell
        {background-color: white; height: 2em;}
.navigation_link
        {padding: 5; color: navy;}
.navigation_link:hover
        {background-color: maroon; color: white; }
.content
        {z-index: 1;}